1. Field of the Invention
The present invention relates to a display, array substrate, and display manufacturing method.
2. Description of the Related Art
In a display such as an organic electroluminescent (EL) display in which the optical characteristics of display elements are controlled by drive currents supplied to the elements, image quality fluctuations such as luminance unevenness occur if the drive currents vary. Therefore, if an active matrix driving method is used in a display like this, the characteristics of drive control elements each of which is included in a pixel and controls the magnitudes of the drive current must be substantially the same. In this display, however, the drive control elements are generally formed on an insulator such as a glass substrate, the characteristics readily vary.
U.S. Pat. No. 6,373,454 describes an organic EL display using a current mirror circuit in a pixel.
This pixel includes an n-channel field effect transistor (FET) as a drive control element, an organic EL element, and a capacitor. The source of the n-channel FET is connected to a low-potential power supply line, and the capacitor is connected between the gate of the n-channel FET and the power supply line. Also, the anode of the organic EL element is connected to a high-potential power supply line.
This pixel is driven by the following method.
First, the drain and gate of the n-channel FET are connected to each other, and an electric current Isig corresponding to a video signal is supplied to the drain-to-source path of the n-channel FET in this state. By this operation, the voltage between the two electrodes of the capacitor is set at a gate-to-source voltage necessary to make the electric current Isig flow through the n-channel FET.
Then, the drain and gate of the n-channel FET are disconnected from each other, and the voltage between the two electrodes of the capacitor is held. Subsequently, the drain of the n-channel FET is connected to the cathode of the organic EL element. As a consequence, a drive current Idrv having a magnitude substantially equal to that of the electric current Isig flows though the organic EL element. The organic EL element emits light at luminance corresponding to the magnitude of the drive current Idrv.
As described above, when the current mirror circuit is used in a pixel, the drive current Idrv having a magnitude substantially equal to that of the electric current Isig supplied as a video signal during a write period can be supplied between the drain and source of the n-channel FET even in a holding period following the write period. This makes it possible to eliminate the influence of not only a threshold value Vth but also the mobility, dimensions, and the like of the n-channel FET on the drive current Idrv.
The present inventor, however, has found that display unevenness may occur even in a display using the current mirror circuit described above in a pixel.